An SRM may have three phases, four phases, or some other number of phases. In some applications, it may be desirable to detect the rotor position in an SRM. In some applications, scheduling the commutation angles in an SRM is a function of rotor position.
Rotor position detection may be direct or indirect. Direct position sensing of a rotor may be done with a position sensor. Indirect position sensing or position estimation of a rotor may be done without a position sensor.
Position sensors may include shaft-mounted encoders or resolvers. A position sensor may sense rotary position based on optical detection, magnetic field variations, or other methodologies. Position sensors may include potentiometers, resolvers, synchros, encoders, and the like, as well as combinations thereof.
Indirect position sensing of a rotor done without a position sensor may be by intrusive methods or non-intrusive methods.
In some embodiments, the intrusive methods involve active probing of the idle phases of an SRM. In some embodiments, the inductances of the SRM phases may be measured by probing signals. In some embodiments, the assumptions and methodology employed in intrusive methods limit applicability at high speeds.
In some embodiments, the non-intrusive methods employ terminal measurements of the phase current and phase voltage of the SRM. In some embodiments, the methodology and assumptions used in this method limits the performance at low, zero, or near zero speeds.
It remains desirable to develop methods of indirect position sensing of the rotor position of a three-phase SRM adequate to address a broad scheme of operational scenarios, including, but not limited to low speeds and high speeds.